In the field of a solar cell, a light-emitting device and a touch panel, a metal oxide film is formed on a substrate. Conventionally, there are Patent Documents 1, 2, and 3 as a non-vacuum film forming technique which forms a metal oxide film on a substrate.
In the technique of Patent Document 1, a metal oxide film is formed on a substrate by bringing a solution in which a metal salt or a metal complex is dissolved into contact with a heated substrate. In this technique, at least one of an oxidizing agent and a reducing agent is contained in the solution.
In the technique of Patent Document 2, a tetrabutyltin solution or a tin tetrachloride solution, in which hydrogen peroxide is added as an oxidizing agent, is sprayed onto a preheated substrate and thermally decomposed. Then, after the substrate temperature lowered by spraying of the solution returns, the solution is sprayed repeatedly. Thereby, a thin film of tin oxide is grown on the surface of the substrate.
In the technique of Patent Document 3, a solution in which a thin film material is dissolved in a volatile solvent is intermittently sprayed toward a substrate kept hot from above to form a transparent conductive film on the surface of the substrate. In this technique, intermittent spraying is high-speed pulsed intermittent spraying in which one spraying duration is 100 milliseconds or less.